The present invention relates to a fluorescent lamp, and more particularly to an improved electrode structure for a fluorescent lamp.
Conventionally, in an electronic copying machine in which image information including figures and/or characters is duplicated on a recording paper by electrophotography, and also in an image processing device such as an image scanner in which the surface of an original is optically scanned so as to convert the image on the original into an electrical signal, a strong light source for illuminating the surface of the original is needed. For this purpose, there has been used a light source such as a fluorescent lamp in which a fluorescent material is activated in such a manner as to cause it to emit light.
Such a fluorescent lamp includes a pair of electrodes mounted at respective opposite ends of a glass tube in opposed relation to each other. Mercury vapor or the like under a low pressure is sealed in the glass tube, and a fluorescent material is coated on the inner surface of the tube. The fluorescent material is not coated on part of the inner surface of the glass tube so as to provide a non-coated region of a predetermined width which extends longitudinally of the glass tube in a slit-like manner to form a light-applying aperture A strong light output can be obtained through this aperture
The above conventional fluorescent lamp suffers from a drawback, however, in that its starting ability (i.e., the ability of being turned on) is inferior in a low-temperature environment, particularly around 0.degree. C.
More specifically, when the fluorescent lamp is at a temperature around 0.degree. C., the mercury in the glass tube tends to liquefy, and therefore even when a predetermined voltage is applied between the electrodes, it is difficult to obtain a proper discharge. As a result, the fluorescent lamp is not immediately lit or turned on.
To deal with this problem, various measures have been taken. One example is to increase the voltage applied between the electrodes, and another is to mount a heater around the glass tube for pre-heating purposes. However, the former is not satisfactory from the viewpoint of compactness of the lamp since the capacity of the power source must be increased. The latter is also unsatisfactory because a warm-up time is required when turning on the lamp. Also, a space for the installation of the heater must be provided, and the electric power consumption is increased.